He will be a bad lover only if being a good poet and being prone to extravagant romantic gestures are the required qualities of a good lover. Benedick tries to write poetry for Beatrice, but it is, frankly, bad poetry. He has no talent for rhyming. He is not prone to extravagant displays of affection and extravagant gifts as well. He feels that he might be a failure at wooing Beatrice if these are quailities she needs in a suitor.